It began with a tip to the CIA eight months ago about a possible Osama bin Laden hiding place, and led Sunday to the bold military operation that will go down in U.S. history, as Navy SEALs killed the Al Qaeda leader in a mansion in Abbottabad, Pakistan while he reportedly used women as human shields.

And the trail that ultimately led U.S. forces to Bin Laden may have begun with another 9/11 plotter who is now in U.S. custody, Khalid Sheikh Muhammad.

Khalid Sheikh Muhammad, central to both the 9/11 plot and the murder of American journalist Daniel Pearl, was captured by U.S. forces and taken to Guantanamo. In 2007, U.S. officials who were interrogating Guantanamo detainees finally learned the real name of a former Khalid Sheikh Muhammad protégé who had become an important confidante of Abu Faraj al Libi. Al Libi was captured in 2005 and also taken to Guantanamo.

Guantanamo detainees identified the courier who had worked with both KSM and Al Libi as someone who was probably trusted by Bin Laden. Al Libi had actually lived in Abbottabad in 2003, according to his detainee file.

In 2007, U.S. officials learned the courier's real name. In 2009, they located his region of operation and began tracking him.

Osama Bin Laden wasn't hiding in a cave, but in a Pakistani city of 90,000 called Abbottabad, just north of the Pakistani capital.

In August 2010, through tracking the courier, they found that Osama Bin Laden probably wasn't hiding in a cave, but in a huge house in the Pakistani city of Abbottabad, just north of the Pakistani capital of Islamabad. The acre-large, million-dollar compound had 12 to 18-foot walls, was eight times the size of other homes in the area and just off a major highway, but had no phones.

President Obama gave the order for a small team of U.S. Navy SEALs in Afghanistan to go in Sunday night Pakistan time, even though bin Laden had never once actually been seen in the compound.

"I determined that we had enough intelligence to take action," said President Obama in a nationally televised address Sunday night, "and authorized an operation to get Osama bin Laden and bring him to justice."

Bin Laden, who had been pictured over the years firing an automatic weapon, and his son and three others opened fire on the U.S. raiders.

Said President Obama, "After a firefight, they killed Osama Bin Laden and took custody of his body."

Pentagon officials said that one way the SEALs were sure it was Osama Bin Laden was that his wife identified him by name.

None of the Americans was injured in the raid.

The U.S. team was on the ground for only 40 minutes, much of the time spent scrubbing the compound for information about al Qaeda and its future plans.

After the raid, blood covered the floor of one room inside the sprawling house on the right. In another room to the left that held a small kitchenette, broken computers could be seen, minus their hard drives

Remarkably, Bin Laden was hiding almost under the nose of the Pakistani military, which has a major garrison in Abbottabad and the Pakistani version of West Point.

U.S. officials say Pakistan was not informed in advance of the military operation inside their borders.